OFDM modem for transmission of continuous complex numbers

ABSTRACT

The invention enables the transmission of continuous complex numbers using a symbol based transmission scheme such as OFDM. Accordingly, complex numbers are mapped to the constellation map, enabling a fine granularity of constellation points. This scheme may be used, for example, in the transmission of video where the coefficients representing the higher frequency of each of the video components, as well as the quantization error values of the DC and near DC components, or some, possibly non-linear transformation thereof, are sent as pairs of real and imaginary portions of a complex number that comprises a symbol.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is continuation of U.S. patent application Ser.No. 11/551,654 filed Oct. 20, 2006 which claims benefit from USProvisional Application 60/729,459 filed Oct. 21, 2005 which isincorporated herein in its entirety by this reference thereto. Thisapplication also claims priority to U.S. Provisional Application60/752,155 filed Dec. 19, 2005 and U.S. Provisional 60/758,060 filedJan. 10, 2006. The disclosures of all these applications, including allappendixes thereof, are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the transmission of uncompressed video over awireless link. More specifically, the invention relates to thedelay-less and buffer-less transmission of uncompressed HDTV video overa wireless link using direct mapping of image transform coefficients totransmission symbols.

2. Discussion of the Prior Art

In many houses, television and/or video signals are received throughcable or satellite links at a set-top box at a fixed point in the house.In many cases, it is desired to place a screen at a point a distancefrom the set-top box by a few meters. This trend is becoming more commonas flat-screen using plasma or liquid crystal display (LCD) televisionsare hung on a wall. Connection of the screen to the set-top box throughcables is generally undesired for aesthetic reasons and/or installationconvenience. Thus, wireless transmission of the video signals from theset-top box to the screen is preferred. Similarly, it may be desired toplace a computer, game controller, VCR, DVD, or other video source thatgenerates images to be displayed on a screen a distance from the screen.

Generally, the data are received at the set-top box compressed inaccordance, for example, with the motion picture expert group (MPEG)format and are decompressed by the set-top box to a high quality rawvideo signal. The raw video signal may be in an analog format or adigital format, such as the digital video interface (DVI) format or thehigh definition multimedia interface (HDMI) format. These digitalformats generally have a high definition television (HDTV) data rate ofup to about 1.5 Giga bits per second (Gbps).

Wireless short range transmission in the home can be done over theunlicensed bands around 2.4 GHz or around 5 GHz (e.g., in the U.S5.15-5.85 GHz band). These bands are currently used by wireless localarea networks (WLAN) where the 802.11 WiFi standard allow maximal datarates of 11 Mbps (802.11b), or 54 Mbps (for 20 MHz bandwidth and the802.11g/802.11a standards). Using the emerging Multi-Input Multi-Outputtechnology the data rate of the emerging 802.11n standard can increaseto above 200 Mbps when a 20 MHz band is used and double of that when a40 MHz band is used. Another alternative is to use Ultra Wide Band(UWB), which claims to provide 100-400 Mbps.

Since the available data rate is lower than the 1.5 Gbps needed foruncompressed HDTV video, the video generally needs to be recompressedfor wireless transmission, when desired. Known strong video compressionmethods, e.g. those having a compression factor of above 1:30 requirevery complex hardware to implement the compression. This is generallynot practical for home applications. These compression methods generallytransform the image into a different domain by using, for example,wavelet, discrete cosine transform (DCT), or Fourier transforms, andthen perform the compression in that domain. The transforms typicallyde-correlate the data to allow for effective compression. In PCTapplication IL/2004/000779, Wireless Transmission of High Quality Video,assigned to common assignee and incorporated herein in its entirety bythis reference thereto, there is shown a method of transmitting videoimages. The method includes providing high definition video, compressingthe video using an image domain compression method, in which each pixelis coded based on a vicinity of the pixel, and transmitting thecompressed video over a fading transmission channel.

In U.S. patent publication 2003/002582 to Obrador there is described awireless transmission of images which are encoded using joint sourcechannel coding (JSCC). The transmitted images are decomposed into aplurality of sub-bands of different frequencies. Image and correspondingboundary coefficients with a lowest resolution are sent first and thenimage and boundary coefficients with a higher resolution aretransmitted. An exemplary JSCC applies channel encoding techniques tothe source coded coefficients, providing more protection to moreimportant, i.e. low frequency, coefficients and less protection to lessimportant, i.e. high frequency, coefficients. Another technique for JSCCwas proposed by Ramstad, The Marriage of Subband Coding and OFDMTransmission, Norwegian University of Science and Technology (July2003), that combines subband coding of the source, for example images,and OFDM modulation.

In digital transmission methods, signals are transmitted in the form ofsymbols. Each symbol can have one of a predetermined number of possiblevalues. The set of possible values of each symbol is referred to as aconstellation and each possible value is referred to as a constellationpoint. The distance between neighboring points affects the immunity tonoise. The noise causes reception of another point instead of theintended point, and thus the symbol may be interpreted incorrectly. Inorthogonal frequency division multiplexing (OFDM) communication scheme,the symbols are comprised of multiple bins, e.g., 64, 128 or 256 bins,in the frequency domain, each bin of each symbol comprised of a twodimensional constellation. It is also known in the art that the use ofsome of the available bins is not recommended. Typically these are thebins located at the ends of the transmission band. Typically, forexample in 802.11a/g, some 16 available channels out of the 64, are notused, and hence the efficiency of the band is reduced.

In U.S. patent application serial no, 2004/0196920 and 200410196404 byLoheit et al. another scheme is proposed for the transmission of HDTVover a wireless link. The discussed scheme transmits and receives anuncompressed HDTV signal over a wireless RF link which includes a clockthat provides a clock signal synchronized to the uncompressed HDTVsignal. This scheme also includes a data regeneration module connectedto the clock, which provides a stream of regenerated data from theuncompressed HDTV signal. A demultiplexer demultiplexes the stream ofregenerated data, using the clock signal, into an I data stream and a Qdata stream. A modulator connected to the demultiplexer modulates acarrier with the I data stream and the Q data stream. According toLoheit et al. the RF links operate at a variety of frequency bands from18 GHz up to 110 GHz, hence requiring sophisticated and more expensivetransmitters and receivers.

In view of a variety of limitations of the prior art it would beadvantageous to provide a solution that enables the reliable wirelesstransmission of an HDTV stream while avoiding the need for aggressive orcomplex compression, or complex hardware implementations. In particularit would be advantageous to avoid a compression that relies on havingframe buffers for reaching the compression levels necessary to transmitthe vast amount of data required in applications, such as wirelesstransmission of HDTV data streams. It would be further advantageous toavoid use of ultra-high frequencies to achieve the goal of wirelesstransmission of an HDTV data stream. It would be of further advantage ifthe proposed system would not insert delays in the transmission of thevideo. It would be further advantageous if a more efficient use of thetransmission band is achieved, thus allowing the transmission of moreinformation.

SUMMARY OF THE INVENTION

The invention enables the transmission of continuous complex numbersusing a symbol based transmission scheme such as OFDM. Accordingly,complex numbers are mapped to the constellation map, enabling a finegranularity of constellation points. This scheme may be used, forexample, in the transmission of video where the coefficientsrepresenting the higher frequency of each of the video components, aswell as the quantization error values of the DC and near DC components,or some, possibly non-linear transformation thereof, are sent as pairsof real and imaginary portions of a complex number that comprises asymbol.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a block diagram of coding system in accordance with thedisclosed invention;

FIG. 2 is a schematic diagram showing an 8-by-8 pixel de-correlationtransform, the grouping of the coefficients, and the mapping into coarseand fine symbol representations in accordance with the disclosedinvention;

FIG. 3 is a table showing the number of coefficients selected from eachof the transformed Y, Cr and Cb of an 8-by-8 pixel conversion inaccordance with an embodiment described in the disclosed invention;

FIG. 4 is a flowchart describing the principles of the disclosedinvention;

FIG. 5 is a flowchart showing handling an HDTV video for wirelesstransmission using OFDM scheme in accordance with the disclosedinvention;

FIG. 6 is a detailed block diagram of a coding system in accordance withthe disclosed invention;

FIG. 7 is a block diagram of the bit manipulation block of a codingsystem in accordance with the disclosed invention;

FIG. 8 is a block diagram of a receiver enabled to receive a video steamtransmitted in accordance with the disclosed invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The disclosed invention is intended to overcome the deficiencies of theprior art solutions by providing a scheme that allows the transmissionof video, such as a high-definition television (HDTV) video, over awireless link using transmission symbols, such as symbols of an OFDMscheme. Specifically, the inventors have realized that it is possible tomap the coefficients of a block of pixels, or a portion thereof, after ade-correlating transformation directly into the transmission symbols.The de-correlation is performed for the purpose of minimizing the energyof the coefficients but without compromising the number of degrees offreedom available. For example, a discrete cosine transform (DCT) isperformed on a block of pixels of each of the Y, Cr and Cb components ofthe video. The Y component provides the luminance of the pixel, whilethe Cr and Cb components provide the color difference information,otherwise known as chrominance. In a preferred embodiment all thecoefficients are transmitted in accordance with the disclosed invention.In another embodiment of the disclosed invention, only a portion of thecoefficients are used for transmission purposes, thereby avoiding thevery high spatial frequency coefficients and keeping the lower spatialfrequency coefficients. Significantly, more of the Y relatedcoefficients are preserved for wireless transmission purposes than thosefor the other two components, as the human eye is more sensitive toluminance then chrominance. Without limitation and for the purposes ofexample only, a ratio of at least three coefficients respective of the Ycomponent may be used for each of the Cr and Cb components, e.g. a ratioof 3:1:1. However, other ratios may be used without departing from thespirit of the disclosed invention. Hence, in accordance with thedisclosed invention emphasis is given to DC and near DC coefficientsover coefficients representing higher frequencies, and coefficientsrespective of luminance receive a preferred treatment over coefficientsrespective of chrominance. Unlike compression techniques of the likes ofJPEG and MPEG, the invention further sends the information of thequantization error over the transmission channel thereby allowing thereconstruction of the video frame and providing an essentiallyuncompressed transmission of video, and in particular high-definitionvideo, over a transmission channel, wired or wireless.

In accordance with the invention, the DC coefficients, or DC proximatecoefficients having a larger value, are represented in a coarse,sometimes referred to as digital, manner, i.e. part of the DC value isrepresented as one of a plurality of constellation points of a symbol.This is achieved by performing a quantization on these values andmapping those quantized values in accordance with the disclosedinvention. The higher frequency coefficients and in addition thequantization errors of the DC and the DC proximate components whose mainpart is presented coarsely, are grouped in pairs, positioning each pairin a point as the real and imaginary values of the complex number, thatprovide the fine granularity, almost analog, value which at an extremefineness provides for a continuous representation of these values.

Optionally, a non-linear transformation, referred to as companding, isperformed on any one of these values that comprise the complex number.Companding is a non-linear transformation of a value. Common compandingfunctions are logarithmic, e.g., A-law and μ-law. The use of thesetechniques effectively provide for a better dynamical range and bettersignal-to-noise ratio in representing the corresponding values. In apreferred embodiment the following companding function may be used:

f(x)=α*sign(x)*√{square root over (|x|)}  (1)

where x is the value of the coefficient and α is a factor designed tomaintain the power of f(x) to be the same as that of x.

Another possible mapping allows the mapping of a number of data valuesto a smaller number of values thereby potentially saving transmissionbandwidth. For example, two numbers are mapped into one number, or threenumbers are mapped into two numbers and the likes. While inserting acertain distortion when the original values are reconstructed, theadvantage is the capability of sending also the less important data onthe limited available bandwidth. In an exemplary two numbers, forexample x₁ and x₂, would therefore be transformed by a function thatwould result in a single value f(x₁,x₂), where f(x₁,x₂) would be furthermultiplied by a factor α, designed to maintain the power after themapping to be the same as prior to the mapping, shown as:

α² E(f ²(x ₁ ,x ₂))=E(x ₁ ²)+E(x ₂ ²)  (2)

where α is the factor designed to maintain the power of f(x₁,x₂) to bethe same as the combined power of x₁ and x₂. In one embodiment of thedisclosed invention the data transferred may be encrypted.

Unlike MPEG and the likes, the invention disclosed herein allows keepingall the coefficients of the de-correlating transform. Therefore thereconstruction at the receiver side is more accurate as more informationis available for such reconstruction. Furthermore, in accordance withthe disclosed invention it is possible to use sub-channels of thetransmission channel, normally avoided so as to provide necessary marginor to avoid interference problems, for the purpose of transmitting thosecoefficient values which receive a lesser representation. Bytransmitting the less important values as determined in accordance withthe disclosed invention, over the normally un-used sub-channels, orsubbands, effectively there is an increase of the available bandwidthfor transmission. In addition some values can be compacted togetherusing the methods described hereinabove.

The constellation points of all the coarse and fine constellations,generated as disclosed above, are arranged as series of complex numbersthat are modulated for the transmission purposes. In a preferredembodiment for wireless communication, but without limitation on thedisclosed invention, orthogonal frequency division modulation (OFDM) isused. In OFDM communication scheme, symbols are comprised of multiplebins, in the frequency domain, each bin of each symbol comprised of atwo dimensional constellation (a complex number). In a communicationsystem having a bandwidth W there are 2W degrees of freedom. If thespectral efficiency ρ is less than 100% then the number of degrees offreedom is 2Wρ per second. Since each complex number contains twodegrees of freedom the number of complex number that can be transmittedis ρW. By using multiple transmission antennas, that require multiplereception antennas, i.e., a multi-in multi-input multi-output (MIMO)system, the transmission rate for a given bandwidth is increased.

Following is a detailed description of the principles of the disclosedinvention. While the invention is described with respect to particularembodiments and respective figures, such are not intended to limit thescope of the invention and are provided for purposes of example only.

FIG. 1 shows an exemplary and non-limiting block diagram of system 100for direct symbol coding in accordance with the disclosed Invention. Thesystem 100 receives the red-green-blue (RGB) components of a videosignal, for example an HDTV video signal. The RGB stream is converted inthe color conversion block 110 to the luminance component Y, and the twocolor difference components, Cr and Cb. This conversion is well known topersons of ordinary skill in the art. In one embodiment of the disclosedinvention, the video begins with a Y-Cr-Cb video signal and, in such acase, there is no need for the color conversion block 110. The Y-Cr-Cbcomponents are fed to a transform unit 120 where a de-correlatingtransformation is performed on blocks of pixels respective of each ofthe three components. In one embodiment of the disclosed invention, theblock 120 performs a DCT on the blocks of pixels. A block of pixels maycontain 64 pixels arranged in an 8-by-8 format, as shown in to FIG. 2.The transform unit 120 may comprise a single subunit for performing thedesired transform, for example a DCT, handling the conversions for allthe blocks of pixels of an entire video frame for each of the Y-Cr-Cbcomponent. In another embodiment, a dedicated transform subunit is usedfor each of the Y-Cr-Cb components, thereby accelerating the performanceof the system. In yet another embodiment a plurality of subunits areused such that two or more such subunits, capable of performing adesired transform on a block of pixels, are used for each of the Y-Cr-Cbcomponents, thus further accelerating the performance of the system 100.The output of transform unit 120 is a series of coefficients which arefed to a mapper 130. The mapper 130 selects those coefficients from eachof the Y-Cr-Cb components which are to be transferred over the wirelesslink. The mapper 130 also maps the coefficients to be sent totransmission symbols, for example, the symbols of an orthogonalfrequency division multiplexing (OFDM) scheme, a process described inmore detail with respect to FIG. 4. The symbols are then transmittedusing a modified OFDM transmitter 140 that handles the mixed nature ofthe symbols having a mix of coarse and fine constellation values, asexplained in more detail with respect to FIG. 2. In one embodiment ofthe disclosed invention, a modified OFDM transmitter 140 is connected toa plurality of antennas for the purpose of supporting a multi-input,multi-output (MIMO) transmission scheme, thereby increasing theeffective bandwidth and reliability of the transmission. A personskilled in the art further appreciate that a receiver, for example thereceiver shown in FIG. 8, adapted to receive the wireless signalcomprising the symbols transmitted in accordance with the disclosedinvention, must be capable of detecting the coarse and finerepresentations of the sent symbols, reconstruct the respectivecoefficients, and perform an inverse transform to reconstructing theY-Cr-Cb components. However, because there is no frame-to-framecompression there is no need for frame buffers in the system. Becausethe mapping and transform are fast and work on small blocks with no needto consider wide area correlation in the image, nor frame-to-framecorrelations, there is practically no delay associated with theoperations disclosed herein, and further more only a limited number oflines need to be kept within frame processing. The components thereceiver are discussed in more detail below.

In accordance with the disclosed invention, a de-correlating transform,such as a DCT, is performed on blocks of pixels, for example 8-by-8pixels, on each of the Y-Cr-Cb components of the video. As a result ofthe transform on a block, for example a block 210 shown in FIG. 2, a twodimensional coefficient matrix 220 is created. The coefficients closerto the origin, in the area 222, are generally the low frequency and DCportions of each of the Y-Cr-Cb components, such as the coefficient222-i. Higher frequency coefficients may be found in the area 224, suchas coefficients 224-i, 224-j, and 224-k, generally having asignificantly smaller magnitude than the DC components, for example lessthan half the amplitude of the DC component. Even higher frequencies maybe found in the area marked as 226. The inventors have noted that, tokeep an essentially uncompressed video, it may be possible to remove thehigh frequency coefficients in the area 226 for each of the Y-Cr-Cbcomponents. The area 226 may be smaller or larger depending, on thenumber of coefficients that may be sent in a particular implementation.The main portion of the DC coefficient, for example the most significantbits of the coefficient 222-i, is preferably mapped into one of aplurality of constellation points, such as shown in the constellationmap 230. A constellation map may be a 4QAM (QPSK), 16QAM, or any otherappropriate type. Because four constellation points 231 through 234 areshown in constellation map 230, a 4QAM implementation is taught in thisembodiment, and each of the constellation points is mapped to a digitalvalue from 00 to 11, respectively. The quantized value of coefficient222-i is mapped to one such constellation point, depending on itsspecific value. Such a mapping is considered a digital value mapping.

However, this coarse representation is also likely to have aquantization error, or in other words, a value corresponding to thedifference between the original value and the value represented by thecoarse representation. This error essentially corresponds to the leastsignificant bits of the high importance coefficients' values that werequantized. The quantization error value, as well as coefficients notrepresented in a coarse manner, i.e., the coefficients associated withthe higher frequencies of area 224, may be mapped as part ofconstellation point 240-i as, for example, the real portion of thecomplex number constituting the symbol 240-i. The higher frequencycoefficients are paired and each pair is mapped to a constellation pointas a real portion and an imaginary portion of a complex number. Forexample, the coefficients 224-i and 224-j may be mapped to the imaginaryand real portions of a constellation point 240-j. This allows for acontinuous representation effectively using any available point in theconstellation mapping, or otherwise providing a fine constellation. Sucha mapping is considered continuous value mapping.

As noted above, a receiver enabled to receive the symbol streamdisclosed herein, such as the receiver shown in FIG. 8, should be ableto recompose the coefficients from the transmitted symbols, and isdiscussed in more detail below. The inventions of MIMO with continuousrepresentation and OFDM with continuous representation provideadvantages over the prior art. Specifically, only simple andstraightforward algebraic computation is necessary for the reception ofthe fine values of the transmitted video stream. Even if some errorsoccur, the impact on the quality of the video stream is quite limitedand generally non-observable. By contrast, MIMO and/or OFDM systemssending pure data, including video transmitted as data rather than thatin the manner disclosed in this invention, requires significantly morecompute power, and more bandwidth, generally not readily available, andthe video quality is more sensitive to errors.

An exemplary reference may be found in FIG. 3, where an 8-by-8coefficient matrix is assumed and, hence, there are 64 coefficientsfound for each of the Y-Cr-Cb components. However, for the reasonsmentioned hereinabove, typically between 28-64 of the coefficients ofthe Y component, and 12-64 of each of the Cr and Cb components aretransmitted over the wireless link. The exact number of coefficients maybe determined based on the available number of OFDM symbols, where eachbin of the OFDM symbol has two degrees of freedom, available forwireless transmission, and on the desired level of reliability of thewireless transmission. A 20 MHz OFDM channel allows for up to 20Mcomplex numbers, 20M real and 20M imaginary, per second, i.e., 40Mdegrees of freedom per second. In a MIMO, that effectively expands theavailable bandwidth, system with four transmission antennas four such 20MHz OFDM channels are made available and hence, theoretically, up to160M numbers, or degrees of freedom per second, are possible. Inpractice full spectral efficiency is not achievable. Due to thetechniques disclosed herein, spectral efficiency of the disclosedsolution is typically ˜75% and hence each transmission channel candeliver about 30M degrees of freedom per second or a total of 120Mdegrees of freedom per second, in the discussed example. In accordancewith the disclosed invention some of the channels are used to transmitthe coarse representation and the rest to transmit the finerepresentation. More degrees of freedom are provided to the moreimportant coefficients while less degrees of freedom are provided to theless important coefficients, or even quantization errors thereof. In anexemplary transmission of an HDTV video a single frame is contained inabout 1200 OFDM symbols corresponding to 256 bins, and which contain theinformation of about 14,400 blocks of 8-by-8 pixels. The use of a 40 MHzbandwidth channel will allow the sending of twice the number ofcoefficients and thus more of the coefficients more accurately, forexample, it may allow sending the coarse information that has higherimportance in a more robust manner, by repeating the information in thecourse of transmission.

FIG. 4 shows an overview flowchart 400 describing the principles thatare at the core of the disclosed invention. In S410 a video streamundergoes a de-correlating transformation. As a result a plurality ofcoefficients describing the components of the original video stream areprovided. In S420 the DC and DC proximate coefficients are selected forthe coarse representation of the transmission in accordance with thedisclosed invention. In S430 a quantization of the coarse representationtakes place and in S440 the quantized coarse representation is mappedonto symbols in accordance with the disclosed invention. In S450 thefine representation comprised of quantization error values from thequantization in S430 as well as the remaining coefficients not selectedin S420 form the fine representation of the transmission in accordancewith the disclosed invention are prepared in one embodiment of thedisclosed invention only a portion of the higher frequency coefficientsare selected for use with respect of the fine representation stream. Inyet another embodiment of the disclosed invention the finerepresentation data, or portions thereof, undergoes non-lineartransformations, as explained in more detail above. In S460 the finerepresentation values are mapped into pairs of real and imaginaryportions of symbols. Lastly, in S470 the created symbols are transmittedin accordance with the disclosed invention.

FIG. 5 shows an exemplary and non-limiting flowchart 500 of the handlingof an HDTV video for wireless transmission using the OFDM scheme inaccordance with the disclosed invention. In S510, a RGB video isreceived. In S520, the RGB is converted to a Y-Cr-Cb video data stream.In one embodiment of the disclosed invention, a Y-Cr-Cb video isprovided and, therefore, the conversions discussed with respect to S510and S520 are not necessary. In S530 a de-correlating transform isperformed, for example DCT, on each of the plurality of blocks ofpixels, for example a block of 8-by-8 pixels, of each of the Y-Cr-Cbcomponents of the video. A plurality of coefficients is created as aresult for each block, for example 64 coefficients in the case of the8-by-8 block. Optionally, in S540, for each of the Y-Cr-Cb components,the number of coefficients to be transmitted is selected. A personskilled in the art would appreciate that in a sense a compaction takesplace in this case. However, the compaction, if performed, takes placeon low coefficient values.

S550 through S570 provide a more detailed description of the mappingprocess discussed with respect to FIGS. 1, 2 and 4 above. In S550, thecoefficients in the DC and DC proximate range are handled. Typically,their amplitude is significantly higher than that of the rest of thecoefficients, i.e., their most significant bits (MSBs) are material forthe information to be sent, and hence these form the coarserepresentation. Therefore, the MSBs of these coefficients are mappedseparately and differently from their respective least significant bits(LSBs), which are otherwise referred to as the quantization error of theDC coefficient. For example, if the coefficient is represented by11-bits, the three MSBs are separated from the rest of the bits as acoarse representation, and transferred as a symbol of its own. In oneembodiment, the coarse representation is repeated in several symbols forthe purpose of ensuring proper and robust reception because the loss ofthis information is significant for the quality of the reconstructedimage. Specifically, the coarse representation is sent as explained inmore detail with respect to FIG. 2 above. In another embodiment errorcorrection code is used to assure the robust reception of these bits.The error correction may further be an unequal error correction which isdescribed in detail in U.S. provisional patent application Ser. No.60/752,155, entitled “An Apparatus and Method for Unequal ErrorProtection of Wireless Video Transmission”, assigned to common assigneeand which is hereby incorporated by reference for all the usefulinformation it may contain. In a further embodiment the more importantcoefficients are represented by more of the MSBs versus othercoefficients represented by fewer MSBs. The LSBs of the DC componentthat (as noted above) have an amplitude described by the LSBs, forexample 8 LSBs of an 11-bit value, as well as the rest of the higherfrequency coefficients, construct the fine representation of thecoefficients and may be mapped as explained with respect of S560 andS570, as further discussed with reference to FIG. 2 above. Each pair ofthe fine representation values may be viewed as the real and imaginarycomponents of a complex value which establishes a symbol of the OFDMscheme. Therefore, if there are 230 available symbols for transmissionin a given time slot, it is possible to send up to 460 pairs of real andimaginary portions of a complex values. However, some 60 symbols areused to send coarse values as explained above. In S580, the symbols aretransmitted over a wireless link using the OFDM scheme. The overallresult of using the steps described herein is to provide a very highframe rate, for example above 45 frames per second, or over 0.6 Gbitsper second of video information, hence allowing for a high qualitytransmission of HDTV video where the video is essentially uncompressed.

The separation to a quantized value referred to as a coarserepresentation and a quantization error referred to as a finerepresentation, for describing the DC and other important transformcoefficients, can be generalized as follows. These coefficients can passvia a quantizer that can take several values, say M=2̂n. Thespecification of the quantizer value, represented by n bits plays therole of the MSB's, or coarse values, above, while the quantizationerror, or fine representation, that is the original value minus thevalue represented by the quantizer, plays the role of the LSB's above.

One embodiment of the disclosed invention makes use of pilots. Commonly,pilots are sent as a priori known signals in some bins of the OFDMsymbol, preferably a value from a QPSK constellation. These pilots,alone or in conjunction with other pilots, are used in standard modemsfor synchronization, frequency, phase corrections, and the like. Pilotscan also help in channel estimation and equalization. In standarddigital modem, these pilots together with the digital informationvalues, the latter being used via decision feedback because these valuesare known to those skilled in the art after decoding, allow robustchannel estimation and tracking. In the invention disclosed herein, theanalog data, sent in the manner discussed in more detail above, makesthe use of decision feedback impossible. Therefore, in accordance withthis embodiment of the disclosed invention additional pilots are sent toensure stable channel estimation and tracking. These pilots may now beused for the purpose of sending the digital data discussed in moredetail above, i.e. the coarse values of some transform coefficients aresent over these pilots. Because additional pilot signals are sent, thereis more room for coarsely represented data. This results in an improvedsignal-to-noise ratio (SNR) on the finely represented data, because evenlarger portion of the transform coefficients, for example the DCTcoefficient, is now sent. Alternatively the higher importancecoefficients can now be sent more than once thereby increasing the noiseimmunity for such high importance coefficients.

FIG. 6 shows an exemplary and non-limiting block diagram 600 of a systemdesigned to handle the coding in accordance with the disclosedinvention. A base band modulator is divided into five basic blocks,according to the functionality and working domain of each bock. Themodulator input consists of four signals: one is a symbol stream of thefine data, the result of the transform discussed in more detail abovewith respect to the handling of the quantization error values of thehigher importance coefficients and those coefficients identified to beof lower importance. The other is a bit stream that represents thecoarse part of the DC values of, for example, Y, Cr and Cb components,and possibly the coarse part of some other components as explained inmore detail above with respect of the MSBs of the coefficients above.These streams are supplied from video coder 610. In addition, there maybe an audio signal, and command signals that come from modem control670. The signals from modem control 670 consists of a number of controlcommands that are to be passed to the receiver, for example the receiverof FIG. 8, as well as other control signals to control the modulator. Inone embodiment of the system 600, the modulator output consists of aplurality of signals, for example four signals, that carry theinformation to digital-to-analog converter 660. This allows for theimplementation of MIMO transmission as discussed above.

FIG. 7 shows an exemplary and non-limiting block diagram of bitmanipulation unit (BMU) 620 of the system 600. The BMU 620 is capable ofperforming all bit manipulations on the data bits themselves. There areno quantization errors handled by the BMU 620, and all operations areperformed bitwise. First, the audio and coarse representation bitstreams are arranged in a predefined order and create a single bitstream by the bit arrangement unit 622. After optional coding byoptional coding unit 624, the bits of the single bit stream are mappedto the desired constellation by B2S mapper 626 and passed to a framerunit 630. The framer unit 630 receives the single bit stream and thefine bit stream as a number of sample streams and organizes it into foursample streams with an appropriate header, pilots, and so on. Twodifferent data streams are padded with pilots and, optionally, with someother data where it may be deemed necessary, and then interleaved. In aMIMO implementation, the stream is divided into a plurality of streams,for example four streams, one for each of the MIMO transmitters. Thefrequency domain unit (FDU) 640 gets its inputs from the framer 530. Theframer 630 creates a symbol stream, such that each symbol is a complexnumber in accordance with the disclosed invention, as describedhereinabove, that represents a point in the two-dimensional space. Theframer 630 also includes an inverse fast Fourier transform (IFFT)operation, and the resultant signal is fed to the time domain unit (TDU)650 where certain shaping of the signal is performed prior to convertingthe signal to an analog signal in the digital-to-analog converter (DAC)660.

The DAC 660 may be operative, in one embodiment of the disclosedinvention, at a sampling rate of 40 MHz, or even higher frequencies, forexample 80 or 160 MHz. The desirable number of bits can be approximatedusing the following assumptions: quantization noise of about 6 dB perbit, peak to average (PAR) of the signal ˜14 dB, symbol SNR for adesired bit error rate (BER) and given constellation ˜22 dB, and asafety margin ˜6 dB. In total, at least seven bits are required,however, to be on the safe side, and according to the limitations ofexisting technology, it is recommended to use, without limiting thegenerality of the disclosed invention; a 10-bit or even 12-bit DAC.

FIG. 8 shows an exemplary and non-limiting receiver 800 adapted toreceive signals transmitted in accordance with the disclosed invention.A demodulator 810 is adapted to receive the symbols transmitted inaccordance with the disclosed invention, for example as OFDM symbols.The reception is performed, for example, by means of receiving awireless transmission received from a plurality of antennas 815.Typically, in a MIMO system, the receiver will have at least one moreantenna over the number of channels, or antennas, used by thetransmitter. The demodulator 810 receives the signals from antennas 815and processed according to principles of linear filtering theory by unit812, that also separates the received streams into the respective coarseand fine streams. Alternatively, the coarse data is decoded directly bya MIMO decoding method, such as sphere decoding, while the fine data isprocess in accordance with linear filtering theory. The fine stream ishandled by the decompanding unit 814 that linearizes the received dataand generates the fine stream data. The coarse stream is handled bydigital demodulator 816 operative in accordance with standard digitalmodulation techniques and that generates the coarse stream data. Thedemodulator provides coarse and fine streams of detected OFDM symbolswhich are then converted by unit 820 to the coefficients byappropriately reconstructing them. Specifically, the information of thequantization errors is added to the respective coarse values toreconstruct the DC and near DC coefficients. Other fine values constructthe high frequency coefficient. The reconstructed coefficients are nowprovided to the inverse transformation unit 830 that generates the Y,Cr, and Cb components of the video transmission. A color converter unit840 further converts the luminance and chrominance inputs into astandard RGB output, if so desired. For purposes of simplicity, elementssuch as, but not limited to, decision feedback equalization, used toovercome channel distortions and enable precise reception, channeltracking, timing and carrier tracking, and other components, are notshown, however, such are part of any operable OFDM receiver, arewell-known in the art, and hence considered part of the receiver. Thereceiver 800 may be further enabled to receive pilot signals andinterpret them as containing data. Such a capability is described indetail in U.S. provisional patent application Ser. No. 60/758,060,entitled “Use of Pilot Symbols for Data Transmission in Uncompressed,Wireless Transmission of Video”, assigned to common assignee and whichis hereby incorporated by reference for all the useful information itmay contain.

Although the invention is described herein with reference to severalembodiments, including the preferred embodiment, one skilled in the artwill readily appreciate that other applications may be substituted forthose set forth herein without departing from the spirit and scope ofthe invention, including, but not limited to, transmission in accordancewith the disclosed invention over a wired medium. The invention may befurther implemented in hardware, software, firmware or any combinationthereof. Accordingly, the invention should only be limited by thefollowing claims. An embodiment may include a computer software productcontaining a plurality of instructions that when executed comprise theinventions disclosed herein.

1. A wireless video transmitter comprising: a symbol mapper to map afirst component of a value associated with a video frame to a fineconstellation point of a fine transmission symbol plane, wherein thefine transmission symbol plane is defined by groups or constellations offine symbol points and there is a direct relation between numericalvalues and spatial proximity of fine symbol points within a given groupor constellation of the plane.
 2. The wireless transmitter of claim 1,wherein the first component of the value is associated with fine videoframe information.
 3. The wireless transmitter according to claim 2,wherein fine video frame information is selected from the groupconsisting of (1) a relatively high order frequency coefficient derivedfrom the video frame, (2) relatively low order bits of a frequencycoefficient derived from the video frame, and (3) relatively low orderbits of a pixel value of the video frame.
 4. The wireless transmitteraccording to claim 1, wherein the mapper is further adapted to map asecond component of the value associated with the video frame to aconstellation point of a conventional transmission symbol plane, whereinthe transmission symbol plane is defined by transmission symbols whichare substantially equally spaced apart.
 5. The wireless transmitter ofclaim 4, wherein the second component of the value is associated withcoarse video frame information.
 6. The wireless transmitter according toclaim 4, wherein the course video frame information is selected from thegroup consisting of (1) a relatively low order frequency coefficientderived from the video frame, (2) relatively high order bits of afrequency coefficient derived from the video frame, and (3) relativelyhigh order bits of a pixel value of the video frame.
 7. The wirelesstransmitter of claim 6, wherein the second component of the value is aproduct of a quantization of the value and the first component is aquantization error value of the quantization.
 8. The wirelesstransmitter of claim 4, wherein said mapper is adapted to map componentsof each of a stream of values associated with one or more video frames.9. The wireless transmitter of claim 8, wherein said transmitter is anOFDM type transmitter and both fine and coarse transmission symbols aretransmitted on the same sub-carrier.
 10. The wireless transmitter ofclaim 8, wherein said transmitter is an OFDM type transmitter and bothfine and coarse transmission symbols are transmitted on differentsub-carriers.
 11. A wireless video receiver comprising: a symbolde-mapper to demap a first received component of a value associated witha video frame using a fine constellation point of a fine transmissionsymbol plane, wherein the fine transmission symbol plane is defined bygroups or constellations of fine symbol points and there is a directrelation between numerical values and spatial proximity of fine symbolpoints within a given group or constellation of the plane.
 12. Thewireless receiver of claim 11, wherein the first component of the valueis associated with fine video frame information.
 13. The wirelessreceiver according to claim 12, wherein fine video frame information isselected from the group consisting of (1) a relatively high orderfrequency coefficient derived from the video frame, (2) relatively loworder bits of a frequency coefficient derived from the video frame, and(3) relatively low order bits of a pixel value of the video frame. 14.The wireless receiver according to claim 11, wherein the demapper isfurther adapted to demap a second component of the value associated withthe video frame using a constellation point of a conventionaltransmission symbol plane, wherein the transmission symbol plane isdefined by transmission symbols which are substantially equally spacedapart.
 15. The wireless receiver of claim 14, wherein the secondcomponent of the value is associated with coarse video frameinformation.
 16. The wireless receiver according to claim 14, whereinthe course video frame information is selected from the group consistingof (1) a relatively low order frequency coefficient derived from thevideo frame, (2) relatively high order bits of a frequency coefficientderived from the video frame, and (3) relatively high order bits of apixel value of the video frame.
 17. The wireless receiver of claim 16,wherein the second component of the value is a product of a quantizationof the value and the first component is a quantization error value ofthe quantization.
 18. The wireless receiver of claim 14, wherein saiddemapper is adapted to demap components of each of a stream of valuesassociated with one or more video frames.
 19. The wireless receiver ofclaim 18, wherein said receiver is an OFDM type receiver and both fineand coarse transmission symbols are received on the same sub-carrier.20. The wireless receiver of claim 18, wherein said receiver is an OFDMtype receiver and both fine and coarse transmission symbols are receivedon different sub-carriers.